1. Field of the Invention
The present invention relates to a method of controlling a radio frequency (RF) coil receiving a magnetic resonance (MR) echo signal in a magnetic resonance imaging (MRI) system and an apparatus for performing the method.
2. Description of the Related Art
A magnetic resonance imaging (MRI) system is an apparatus for obtaining a tomogram of a subject by indicating an intensity of a radio frequency (RF) signal having a predetermined frequency, which is generated from a magnetic field having a predetermined intensity, by using contrast.
FIG. 1 is a diagram showing a general MRI system in the prior art.
A patient is examined in a cylindrical gantry inside a shield room with shielding to prevent entry of any external RF signal from interfering with the RF signals used in the MRI procedure. A static magnetic field is formed in the gantry by a main magnet. A gradient coil 102 transmits a magnetic field gradient pulse to form a magnetic gradient field. An RF transmitter 101 applies an RF excitation signal having a predetermined frequency to the patient in order to obtain a tomogram of a predetermined portion of the patient. A magnetic resonance (MR) echo signal, generated due to magnetic resonance from the predetermined portion of the patient, is received by an RF coil 103 and is transmitted to a central controlling apparatus 100 in an operating room that is separated from the shield room. Signal processing is performed on the MR echo signal to obtain an MR image. An order of pulses (such as RF excitation signals or the magnetic gradient field), analyzed for obtaining the MR image, is referred to as a pulse sequence. The central controlling apparatus 100 controls the pulse sequence.
In general, the RF coil 103 uses a highly sensitive coil and a high-magnification amplifier in order to receive the MR echo signal having a very low intensity. Since the intensity of the RF excitation signal is several tens of thousands times higher than that of the MR echo signal, if the RF excitation signal is received by the RF coil 103, the RF coil 103 may be damaged. Thus, the following method has been used in the prior art such that, when the RF excitation signal is transmitted, the RF coil 103 does not receive the RF excitation signal by decoupling the RF coil 103 and the RF excitation signal. In addition, when the RF excitation signal is completely transmitted, the RF coil 103 receives the MR echo signal at a correct time. If an error arises in terms of a point of time when the MR echo signal is received, an artifact may appear in the MR image, so controlling the RF coil 103 at a correct time is a very important factor for determining the quality of the MR image.
Recently, research has been conducted into wireless communication between the gantry of the shield room and the central controlling apparatus 100 of the operating room. In the above-described method, analog-digital conversion of the MR echo signal is performed in the shield room, thereby minimizing noise due to an analog cable. That is, the central controlling apparatus 100 wirelessly controls decoupling of the RF coil 103 and receipt of the MR echo signal. Amplification of the MR echo signal received by the RF coil 103 and demodulation to a base band, as well as conversion to a digital signal, are performed inside the shield room. In addition, a digital signal is transmitted to the central controlling apparatus 100 and a signal processing apparatus through a wireless channel.
However, according to such a conventional wireless communication method in the prior art, when the RF coil 103 is not controlled at a correct time, the quality of an MR image may deteriorate. Since a delay due to demodulation and analog-digital conversion for wireless communication, and a delay occurring in a wireless channel are not constant, it is impossible to accurately control the RF coil 103 in real time. For example, since a general IEEE 802.11 based wireless local area network (LAN) assigns a time slot to a plurality of stations by using a time division method, it is difficult for an MRI system to ensure a quality of service (QoS) required to obtain an image having good quality. Thus, it is difficult to control the RF coil 103 in the prior art at a correct time.
In addition, a conventional wireless communication method in the prior art is a synchronization-type method in which decoupling of the RF coil 103 and receipt of the MR echo signal are controlled by the central controlling apparatus 100. In such a synchronization-type wireless MRI system, since the RF coil 103 is controlled in real time, even if an error in terms of data transmission arises during a wireless communication process, it is difficult to correct the error or to retransmit data due to a time delay that is likely to occur. As a result, the RF coil 103 may be damaged or the quality of an MR image may deteriorate.